Apparatus and method for dispensing discrete amounts of viscous material

ABSTRACT

Apparatus and methods for dispensing small amounts of a viscous material onto a workpiece. The narrow-profile dispensing apparatus includes a fluid chamber, a nozzle, and a valve seat disk representing individual components that are removable from a main body of the dispensing apparatus for cleaning and/or replacement. The nozzle is coupled with the fluid chamber by a heat transfer body that may be cooled by, for example, a cooling fluid routed through an air pathway defined in the heat transfer body. The main body of the dispensing apparatus may be cooled by air exhausted from an air cavity of a pneumatic actuator regulating the movement of a needle to control the flow of viscous material in the dispensing apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/328,378,filed Jan. 9, 2006, which is a continuation of Serial No.PCT/US2004/020247 filed Jun. 25, 2004, which claims the benefit of U.S.Provisional Application No. 60/487,034, filed on Jul. 14, 2003. Thedisclosure of each application is hereby incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to dispensing apparatus andmethods and, in particular, to apparatus and methods for dispensingdiscrete amounts of viscous materials in a non-contact manner onto aworkpiece.

BACKGROUND OF THE INVENTION

In the manufacture of microelectronic hardware and other products,pneumatic dispensing apparatus are used to dispense small amounts ordroplets of a highly viscous material in a non-contact manner onto asubstrate or workpiece. Exemplary highly viscous materials include, butare not limited to, solder flux, solder paste, adhesives, solder mask,thermal compounds, oil, encapsulants, potting compounds, inks, andsilicones. Generally, such highly viscous materials cannot easily flowunder their own weight at room temperature.

Conventional pneumatic non-contact dispensing apparatus for viscousmaterials include an air-operated valve element reciprocated forselectively engaging a valve seat surrounding a discharge passageway. Ina process commonly referred to as jetting, droplets are dispensed byretracting the needle from contact with the valve seat, which allows anamount of the viscous material to flow under pressure from a filledfluid chamber through a gap separating the needle from the valve seatand into the discharge passageway. The needle is then moved rapidlytoward the valve seat to close the dispensing apparatus, which causesthe amount of viscous material to be forced through the dischargepassageway and a comparable amount of the viscous material to be ejectedfrom a discharge orifice of the discharge passageway. The small amountof ejected viscous material is propelled as a droplet toward aworkpiece, which is spaced from the discharge outlet.

Valve seat replacement and cleaning in conventional non-contactdispensing apparatus is a time consuming and painstaking process as theinternal surfaces of the dispensing apparatus are difficult to accesswith cleaning tools. Generally, the valve seat is integral with thefluid chamber and, as a result, is non-removable, which restricts accessto the fluid chamber and creates a circular right angle corner at theirjuncture that is difficult to clean. In addition, the valve seat mayinclude guide fingers or vanes that guide the needle so that a needletip makes a reproducible fluid seal with the valve seat tolerant ofminor misalignments. However, the guide vanes define right angle cornersthat are difficult to adequately clean effectively in a short time.

Disassembling and reassembling conventional non-contact dispensingapparatus is a difficult process that involves numerous tools. Inaddition, gauges are required to establish accurate spatialrelationships between components during reassembly. As a result of thecomplexity, disassembly and reassembly are slowed and may take as longas forty-five (45) minutes to complete, even for technicians skilled inthe assembly procedure.

In certain conventional dispensing apparatus, the valve seat in thefluid chamber and the tip of the needle constitute a matched paircarefully lapped to have corresponding dimensional attributes. Anyattempt to replace the valve seat to, for example, change the diameterof the discharge passageway often results in leakage because the needletip and the new valve seat are not a matched pair and, therefore, cannotprovide an adequate seal. In such conventional dispensing apparatus,therefore, the diameter of the dispensing orifice may be changed only byreplacing the existing needle and valve seat with a needle having aneedle tip matched during manufacture with the valve seat.

Another problem encountered in conventional pneumatic non-contactdispensing apparatus is noise. The dispensing apparatus is opened andclosed by switching a solenoid valve to provide and remove pressurizedair from an air piston cavity. The pressurized air acts on an air pistonthat reciprocates the needle. To close the dispensing apparatus, thesolenoid valve is switched to exhaust air pressure from the air pistoncavity to the ambient environment through an exhaust passageway. Therapid flow of air through the exhaust passageway causes sound audible tobystanders. A conventional silencer or muffler may be used to reducenoise at valve exhaust ports. However, the exhaust port of the solenoidvalve must be accessible to permit attachment, typically by a threadedconnection, of the muffler.

It would be desirable, therefore, to provide a dispensing apparatus thatovercomes these and other deficiencies of conventional dispensingapparatus for viscous materials, as described herein.

SUMMARY

In an embodiment of the invention, an apparatus includes a main bodyincluding a discharge outlet, an air cavity, and a valve element movableby selective application of pressurized air to the air cavity between anopened position in which a flow of a viscous material is directed to thedischarge outlet for dispensing and a closed position in which the flowof the viscous material to the discharge outlet is blocked. Theapparatus further includes a solenoid valve having an exhaust portselectively coupled in fluid communication with the air cavity at leastwhen the valve element is moving from the opened condition to the closedposition. Extending through the main body is an air passageway coupledby the exhaust port of the solenoid valve with the air cavity of themain body. Pressurized air exhausted from the air cavity flows throughthe air passageway to cool the main body.

In another embodiment of the invention, an apparatus includes a coolantgas source, a dispensing body including a discharge passageway receivinga flow of a viscous material, and a heat transfer member thermallycoupled with the dispensing body. A temperature sensor is thermallycoupled with the heat transfer member. A controller is electricallycoupled with the temperature sensor and with a cooling means for coolingthe heat transfer member. The controller causes the cooling means tocool the heat transfer member and the dispensing body in response totemperature signals received from the temperature sensor.

In yet another embodiment of the invention, a valve seat disk for adispensing apparatus includes a body having a passageway, an inlet tothe passageway positioned to receive a flow of a viscous material fromthe dispensing apparatus, and a valve seat surrounding the passageway.The valve seat is capable of being contacted by the valve element toblock the flow of the viscous material into the passageway. The inlet isspaced from the passageway such that the valve element does not contactthe inlet.

In yet another embodiment of the invention, an apparatus for dispensinga viscous material includes a main body, a fluid chamber housingremovably attached to the main body, and a nozzle removably attachableto the fluid chamber housing. The nozzle includes a discharge passagewayselectively coupled in fluid communication with a fluid chamber definedby the fluid chamber housing when the nozzle is attached to the fluidchamber housing. Removably positioned inside the fluid chamber housingis a liner covering an inner wall of the fluid chamber housing so thatthe inner wall is not contacted by the viscous liquid.

In yet another embodiment of the invention, a nozzle assembly for adispensing apparatus includes a nozzle and a valve seat disk having adischarge passageway coupled with a discharge passageway of the nozzle.The valve seat disk includes a valve seat positioned to be contacted bya valve element of the dispensing apparatus to block a flow of a viscousmaterial. The nozzle assembly further includes a fluid chamber housingcontaining the viscous material for flow into the discharge passagewayof the valve seat disk when the valve element is open and a retainerremovably mounted to the dispensing apparatus. The retainer secures thevalve seat disk, the fluid chamber housing, and the nozzle to thedispensing apparatus with the valve seat disk positioned between thenozzle and the fluid chamber.

In yet another embodiment of the invention, a nozzle assembly includes adispensing body with a discharge passageway positioned to receive a flowof a viscous material from a dispensing apparatus. The dischargepassageway has a discharge outlet from which the viscous material isdischarged. The nozzle assembly further includes a heat transfer bodyremovably attaching the dispensing body to the dispensing apparatus. Theheat transfer body has a fluid passageway adapted to receive a flow ofthe coolant gas and positioned such that the flow of the coolant gasexiting the fluid passageway does not impinge the viscous materialdischarged from the discharge passageway.

In yet another embodiment of the invention, a nozzle assembly includes adispensing body having a discharge passageway, and a valve seat diskhaving a discharge passageway coupled with the discharge passageway ofthe dispensing body, and a valve seat. The valve seat is positioned tobe contacted by a valve element of a dispensing apparatus to block theflow of viscous material to the discharge passageway of the valve seatdisk. The nozzle assembly further includes a heat transfer bodyremovably securing the dispensing body and the valve seat with thedispensing apparatus such that the valve seat disk is positioned betweenthe dispensing body and the valve element.

In yet another embodiment of the invention, a method of dispensing aviscous material includes directing the viscous material through adischarge passageway in a nozzle, sensing a temperature of the nozzlewith a temperature sensor inside the nozzle, and comparing the sensedtemperature of the nozzle with a set point temperature. If thetemperature of the nozzle is greater than the set point temperature, thenozzle is actively cooled.

In yet another embodiment of the invention, a method of dispensing aviscous material includes exhausting pressurized air from a pneumaticactuator to discontinue a flow of the viscous material discharged from adispensing apparatus. The method further includes cooling a portion ofthe dispensing apparatus by directing the exhausted air through an airpassageway defined in the dispensing apparatus.

These and other objects and advantages of the present invention shallbecome more apparent from the accompanying drawings and descriptionthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the principles ofthe invention.

FIG. 1 is a perspective view of a dispensing apparatus in accordancewith an embodiment of the invention;

FIG. 2 is a top view of the dispensing apparatus of FIG. 1 shown withthe electrical cable and pneumatic conduits absent for clarity;

FIG. 3 is a cross-sectional view of the dispensing apparatus takengenerally along line 3-3 in FIG. 1;

FIG. 3A is an enlarged view of a portion of FIG. 3;

FIG. 4 is an enlarged view of a portion of FIG. 3A;

FIG. 5A is a view of a needle tip and a valve seat disk in accordancewith an embodiment of the invention;

FIG. 5B is a view similar to FIG. 5A, with the needle tip removed forclarity, demonstrating the plastic deformation of the valve seat diskabout the valve seat after contact with the needle tip in the closedposition;

FIG. 6 is a side view of an alternative embodiment of a needle tip foruse in the dispensing apparatus of FIG. 1;

FIG. 7 is a perspective view of an embodiment of a thermal barrierseparating and thermally isolating the solenoid valve from the mainbody;

FIG. 8 is a partial cross-sectional view of an alternative embodiment ofa fluid chamber housing for use with the dispensing apparatus of FIG. 1;

FIGS. 9A and 9B are top and cross-sectional views of an alternativeembodiment of a valve seat disk for use in the dispensing apparatus;

FIG. 10 is a perspective view of a fluid tube heater in accordance withan embodiment of the invention; and

FIG. 11 is a cross-sectional view similar to FIG. 3A in accordance withan alternative embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a dispensing apparatus 10 for use witha computer-controlled non-contact dispensing system (not shown) isshown. The dispensing apparatus 10 of the invention may be installed indispensing systems including those similar, or identical to, thedispensing systems described in U.S. Pat. No. 5,747,102 entitled “Methodand Apparatus for Dispensing Small Amounts of Liquid Material”, thedisclosure of which is incorporated herein by reference in its entirety.Dispensing apparatus 10 is particularly useful when installed in theAsymtek X-1010 Axiom™ SMT Dispenser, the Asymtek X-1020 Axiom™Semiconductor Dispenser, the Asymtek M-2020 Millennium® Ultra High SpeedSemiconductor Dispenser, or the Asymtek M-2010 Millennium® Ultra HighSpeed SMT Dispenser. The dispensing apparatus 10 includes a mount 11,illustrated in FIGS. 1 and 2 as a dovetail mount, for attachingdispensing apparatus 10 to a mechanical support of the dispensingsystem.

The dispensing apparatus 10 includes a module, generally indicated byreference numeral 12, partially positioned inside of a main body 22 andpartially projecting from opposite ends of main body 22, a syringeholder 16 supporting a supply device 14, a solenoid valve 20, and ajunction box 18 positioned between the syringe holder 16 and thesolenoid valve 20. An electrical cable 21 and fluid conduits 23, 25servicing the dispensing apparatus 10 are interfaced to apparatus 10 atthe junction box 18, which acts as a centralized distribution point forpower and fluid to module 12 and solenoid valve 20. The opposite end ofthe electrical cable 21 is coupled with a controller 27 (FIG. 3) of thedispensing system that controls the operation of the dispensingapparatus 10. Fluid conduit 23 supplies pressurized air to a fluidmanifold inside the junction box 18 coupled to solenoid valve 20, whichis energized and de-energized by electrical signals supplied fromcontroller 27 over electrical cables 21 and 29 to supply pressurized airfor opening and closing the pneumatically-operated dispensing apparatus10.

Generally, the controller 27 may comprise any electrical controlapparatus configured to control one or more variables based upon one ormore inputs. A number of individual control systems may be used tocontrol various components (e.g., solenoid valve 20, coolant gas supply85, etc.), and these individual control systems may be integrated, orotherwise considered to collectively constitute, a single combinedcontroller 27. An exemplary controller 27 includes programmable logiccontrol (PLC) devices having easily used human machine interfaces (HMI),as are known to persons of ordinary skill in the art.

The dispensing apparatus 10 is operative for dispensing pressurizedviscous material supplied from a syringe-style supply device 14.Generally, supply device 14 is a disposable syringe or cartridge, andthe viscous material filling supply device 14 is any highly-viscousmaterial including, but not limited to, solder flux, solder paste,adhesives, solder mask, thermal compounds, oil, encapsulants, pottingcompounds, inks, and silicones. The supply device 14 typically includesa wiper or plunger (not shown) movable upon application of air pressure,typically between 5 psi and 30 psi, in the head space above the plunger.

The dispensing apparatus 10, the syringe holder 16, the junction box 18and the solenoid valve 20 are aligned with a generally planararrangement to define a reduced overall width profile, when thesecomponents are viewed in at least one direction, that increases theoverall dispense envelope. Specifically, the total length, L, of thedispensing apparatus 10, including the main body 22, the syringe holder16, the junction box 18 and the solenoid valve 20, is conventional butthe width, W, of dispensing apparatus 10 is significantly reduced ascompared with conventional dispensing apparatus. Generally, the width ofthe dispensing apparatus 10 is about 1.2 inches. Because of the compactwidth, larger workpieces can be processed by multiple dispensingapparatus 10 arranged in a side-by-side relationship (i.e., the overalldispense area is increased).

With continued reference to FIGS. 3 and 3A, the dispensing apparatus 10also includes a valve element, illustrated as a needle 24, axiallymovable within a longitudinal bore 26 of the main body 22, a fluidchamber housing 28, and a nozzle assembly, generally indicated byreference numeral 34. The nozzle assembly 34 includes a nozzle 35 and aheat transfer member 44 having a slip fit with an exterior portion ofthe fluid chamber housing 28. A retainer 32, which includes a collar 30and a wave spring 36 secured to the retainer 32 by a spring clip,removably secures the fluid chamber housing 28 to the main body 22. Theheat transfer member 44 participates with the retainer 32 for securingthe nozzle 35 and a valve seat disk 62 with the fluid chamber housing28.

A portion of the collar 30 has a threaded engagement with the main body22. Extending axially from the retainer 32 is a pair of hooked arms 39a, 39 b (FIG. 1) that engage a rim of heat transfer member 44 forcapturing the heat transfer member 44 with the fluid chamber housing 28.Rotation of the retainer 32 relative to the valve body aligns the hookedarms 39 a, 39 b with slots in the upper rim of the heat transfer member44, at which time a downward force can remove the heat transfer member44 from the fluid chamber housing 28. Nozzle 35 and valve seat disk 62are then removable tool-free as individual parts, as shown in phantom inFIG. 3. The fluid chamber housing 28 may then be removed from the mainbody 22 without the assistance of tools. The ease of removing thesecomponents reduces the time required for disassembly and reassembly toclean internal wetted surfaces and to perform maintenance. When thevalve seat disk 62, the nozzle 35, and optionally the fluid chamberhousing 28, are removed from main body 22, the setting of the preloadingspring bias applied to needle 24 is preserved so that the setting isreestablished when these components are reassembled.

As an alternative to cleaning the fluid chamber housing 28, an existingfluid chamber housing 28 may be removed from the main body 22 andreplaced by a new or cleaned fluid chamber housing 28. In particular,the dispensing apparatus 10 may be provided with a set of fluid chamberhousings 28 that are interchangeable and that may be periodicallyreplaced. Removed fluid chamber housings 28 may be cleaned for re-useor, optionally, discarded.

With reference to FIGS. 3, 3A and 4, the nozzle 35 consists of a nozzletip 46 joined with a nozzle hub or mount 48. The nozzle tip 46 isinserted into a centered axial bore 50 extending along the axialdimension of the nozzle mount 48 and secured by, for example, epoxy orbrazing. A truncated conical or frustoconical surface 54 of the nozzlemount 48 contacts a corresponding truncated conical or frustoconicalsurface 52 of the heat transfer member 44 when the heat transfer member44 is installed on the fluid chamber housing 28 and tightened.Frustoconical surface 52 transfers an axial load to the frustoconicalsurface 54 that secures the nozzle 35 to the fluid chamber housing 28 ina fluid-tight relationship. In one embodiment of the invention, thefrustoconical surfaces 52, 54 are each tapered with an included angle ofabout 70°.

The interface between the frustoconical surfaces 52, 54 promotesefficient heat transfer from the heat transfer member 44 to the nozzle35 by increasing the surface area over which contact exists between theheat transfer member 44 and the nozzle mount 48. Consequently, thefrustoconical interface improves the heat transfer efficiency from theheating element 84 to viscous material flowing inside liquid passageway72 in the nozzle 35. In addition, the engagement between thefrustoconical surfaces 52, 54 operates to self-center the heat transfermember 44 relative to the nozzle mount 48 during installation.

A fluid tube 56 of a conventional construction couples an outlet port ofthe supply device 14 with an inlet port 58 of a fluid chamber 60 definedinside the fluid chamber housing 28. Viscous material is supplied underpressure from the supply device 14 through fluid tube 56 to inlet port58 and ultimately to fluid chamber 60. Fitting 134 provides an interfacebetween the fluid tube 56 and the inlet port 58.

With continued reference to FIGS. 3, 3A and 4, positioned within thefluid chamber 60 is the valve seat insert or disk 62, which is capturedby the axial load applied by the frustoconical surface 52 to thefrustoconical surface 54 in a space defined between the nozzle mount 48and the fluid chamber housing 28. The valve seat disk 62 is removablefrom the dispensing apparatus 10 by removing the heat transfer member 44and the nozzle 35 from the fluid chamber housing 28. Removal of thevalve seat disk 62 will also provide access to the fluid chamber 60 forcleaning.

The fluid chamber housing 28, nozzle 35, and valve seat disk 62 aremodular components bearing surfaces in the dispensing apparatus 10wetted by the viscous material and that are easily removable forcleaning. As a result, the cleaning process for the dispensing apparatus10 is simplified and the overall cleaning time is reduced. In certainembodiments, the entire cleaning process, including disassembly andreassembly of fluid chamber housing 28, nozzle 35, and valve seat disk62, takes about four to five minutes, which is an order of magnitudefaster than comparable cleaning processes for conventional dispensingapparatus. Routine cleaning and maintenance are simplified by a dramaticreduction in the number of tools required to disassemble and re-assemblethe fluid chamber housing 28, nozzle 35, and valve seat disk 62. Thefluid chamber housing 28, nozzle 35, and valve seat disk 62 may bereplaced by comparable clean components and then batched cleaned forfurther reducing the time required to clean these components. In certainembodiments, the fluid chamber 28 may be formed from an inexpensivedisposable material to further simplify maintenance as cleaning isavoided.

The valve seat disk 62 comprises a fluid passageway 64 of a suitablediameter extending between an outlet 66 and an inlet 68. In a newcondition, the inlet 68 defines and coincides with a valve seat 70. In aused condition in which the material of the valve seat disk 62surrounding the inlet 68 has been plastically deformed by contact withneedle tip 76, the inlet 68 and valve seat 70 may differ in location, asdescribed herein. In an alternative embodiment of the invention, thevalve seat disk 62 may be integral with the nozzle mount 48 of thenozzle 35 and, therefore, removable from the dispensing apparatus 10 asa unit or single piece with the nozzle mount 48.

The nozzle tip 46 is tubular and surrounds a discharge passageway 72that is coaxial with the outlet 66 from the fluid passageway 64 in thevalve seat disk 62. Discharge passageway 72 has a relatively high aspectratio, which is determined by the ratio of the length of passageway 72to the diameter of a discharge outlet or orifice 74, so that the nozzletip 46 is lengthy and narrow as compared with conventional nozzle tips.Preferably, ratio of the length of the discharge passageway 72 to thediameter of discharge orifice 74 is greater than or equal to about 25:1.In certain embodiments of the invention, the diameter of dischargeorifice 74 may be one (1) mil to eight (8) mils and the length of nozzletip 46 may be 0.375 of an inch.

This relatively large aspect ratio permits the nozzle tip 46 to accesscrowded dispense areas on a workpiece previously inaccessible toconventional dispensing apparatus due to contact between the nozzle tip46 or another portion of the dispensing apparatus and the workpiece towhich the viscous material is being applied. Specifically, the largeaspect ratio of the permits the nozzle tip 46 to protrude from thenozzle mount 48, as compared with conventional dispensing nozzles.Increasing the aspect ratio increases the length of nozzle tip 46 thatmay protrude from the nozzle mount 48. The nozzle tip 46 may be formedfrom any suitable material including but not limited to tungsten andceramics that are resistant to damage if contacted by an object in theenvironment surrounding the dispensing apparatus 10. The nozzle tip 46may also include a layer 46 a of thermally insulating material, such asa coating, that reduces heat loss from the nozzle tip 46. The insulationprovided by layer 46 a would serve to stabilize the temperature of theviscous material resident in discharge passageway 72. The high aspectratio of the nozzle tip 46 provides sufficient space for providing thelayer 46 a without otherwise interfering with dispensing operations.

The discharge passageway 72 is tapered (or narrowed) along its length ina direction extending toward the discharge orifice 74 from which theviscous material is discharged so that the diameter is narrowestproximate to the orifice 74. Tapering the discharge passageway 72permits the aspect ratio to be increased without introducing asignificant pressure drop over the passageway length and therebycompensates for the non-conventional length of discharge passageway 72by increasing the velocity of the dispensed viscous material at thedischarge orifice 74. The outer diameter of the nozzle tip 46 may besubstantially uniform over most of the tip length.

With reference to FIGS. 3, 3A, 4, 5A and 5B, a lower end of the needle24 includes a needle tip 76 adapted for sealing engagement with valveseat 70 to prevent liquid flow from the fluid chamber 60 into the fluidpassageway 64. An end of the needle 24 opposite to the needle tip 76 issecured with a bore in an air piston 78 that is slidably movable withinan air cavity 80 formed in the main body 22. An annular seal carried bythe air piston 78 provides a fluid-tight sliding seal with a cylindricalsurface surrounding the air cavity 80. Pressurized air selectivelyprovided to the air cavity 80, as explained below, provides forcontrolled, reciprocating movement of needle tip 76 into and out ofsealing engagement with valve seat 70. With needle tip 76 positioned ina retracted position away from valve seat 70, an amount of viscousmaterial flows from the fluid chamber 60 through the fluid passageway 64of valve seat disk 62 and through the discharge passageway 72 of nozzletip 46. A comparable amount of viscous material separates from thedischarge orifice 74 to define a droplet 71 (FIG. 1) because of rapidmovement of the needle tip 76 toward and into contact with the valveseat 70. The airborne droplet 71 of viscous material is propelled fromthe discharge orifice 74 toward, and deposited on, a workpiece (notshown), such as a printed circuit board.

The needle tip 76 is substantially spherical for making a sealingcontact with the circular valve seat 70. Typically, the radius of theneedle tip 76 is selected according to the dimensions of the valve seat70 and the fluid passageway 64 in the valve seat disk 62 so that asealing engagement is provided. As the valve seat 70 wears and/orplastically deforms, the sealing engagement may transform from aline-of-contact to an annular contact surface.

With reference to FIG. 6 and in accordance with an alternativeembodiment of the invention, the dispensing apparatus 10 may be providedwith a needle 24 a having a needle tip 82 characterized by a convexcurvature capable of forming an effective sealing engagement withmultiple different valve seat disks 62 among which the inlet 68 andvalve seat 70 differs in diameter. In one specific embodiment, theneedle tip 82 may have a radius of curvature of about one (1) inch,which effectively seals valve seats 70 on valve disks 62 with dischargepassages 64 ranging from 0.010″ to 0.060″ in diameter. Thisadvantageously provides the ability to change the size of the dispenseddroplet over a greater range without also changing the needle 24 a,which improves the flexibility and range of the dispensing apparatus 10.Additionally, the relatively large radius of curvature of needle tip 82has been sized to tolerate off-axis misalignment between needle tip 82and valve seat 70.

With reference to FIGS. 3A, 4, 5A and 5B, the valve seat disk 62, or atleast a central portion of the valve seat disk 62 including the valveseat 70, is formed from a material, such as 440C stainless steel or 303stainless steel, that is softer than the material forming the needle tip76. As a result, the valve seat 70 wears faster than the needle tip 76and the operating lifetime of the needle 24 is increased. An unusedvalve seat disk 62 includes a circular valve seat 70 coincident withinlet 68, as shown in FIG. 5A. When the needle tip 76 repeatedly strikesthe valve seat 70 in the closed position during the initial dispensingcycles, the valve seat 70 deforms plastically to correlate or conformwith the shape of the needle tip 76, as shown in FIG. 5B. The plasticdeformation or coining defines an annular surface of contact between thevalve seat 70 and needle tip 76 and eliminates the need to match lap theneedle tip 76 and valve seat 70. The valve seat 70 does not coincidewith the inlet 68 after the plastic deformation occurs, although theinvention is not so limited. The valve seat disk 62 is interchangeableand replaceable without the need to also replace the needle 24. Theconforming nature of the valve seat disk 62 eliminates the need tosimultaneously lap the valve seat 70 of valve seat disk 62 and theneedle tip 76 to form a matched pair, as is true in conventionaldispensing apparatus.

If the valve seat 70 is damaged or worn out or to simply change thediameter of the fluid passageway 64, a new valve seat disk 62 may beinstalled without also installing a new needle 24. The needle tip 76 ofthe existing needle 24 will deform the valve seat 70 of the replacementvalve seat disk 62 to establish a sealing engagement therebetween andeffectively preserve the axial alignment therewith despite the exchange.Misalignments radial or transverse to the longitudinal axis of needle 24in the lateral location of the needle tip 76 in relation to the valveseat 70 are accommodated by the deformation of the valve seat 70.

With reference to FIGS. 3 and 3A, a heating element 84, which may be aflexible thermal foil resistance heater, surrounds the exterior of theheat transfer member 44. The heating element 84 has an efficient heattransfer or thermal contact relationship with the heat transfer member44 for heating the heat transfer member 44. Heat is readily transferredfrom the heat transfer member 44 to the nozzle mount 48 for locallyheating the nozzle tip 46 and the viscous material resident in thedischarge passageway 72. In certain embodiments of the invention, theexterior of the heating element 84 and/or the heat transfer member 44may be covered by a layer of thermal insulation 84 a that limits heatloss from heating element 84, which aids in temperature control.

Heat transfer member 44 further incorporates an inlet passageway 86, anoutlet passageway 88, and an annular plenum 90 (FIG. 3A) coupling theinlet and outlet passageways 86, 88 and surrounding an axial length ofthe nozzle mount 48. A coolant gas, such as air, is supplied to inletpassageway 86 from a coolant fluid supply 85 via air conduits 25 and 83,which are coupled inside the junction box 18. The coolant gas flows fromthe inlet passageway 86 through the annular plenum 90 and is exhaustedthrough the outlet passageway 88 to create a positive fluid flow. Thedimensions of the inlet and outlet passageways 86, 88 and the annularplenum 90 are preferably chosen to optimize heat transfer to the flowingcoolant gas. The invention contemplates that the coolant gas may beprovided in a different manner or cooling may be accomplished using adifferent cooling fluid, such as a liquid. In an alternative embodimentof the invention, the heat transfer body 44 may be cooled using athermoelectric cooling device 93 (FIG. 4A), such as a Peltier cooler.

A temperature sensor 92 (FIG. 3A), such as a resistance temperaturedetector, is disposed in a blind sensor passageway 94 (FIG. 3A) definedin the heat transfer member 44. The temperature sensor 92, which ispositioned in heat transfer member 44 proximate to the heating element84, provides a temperature feedback signal over a set of leads 87, 89 tocontroller 27. Leads 87, 89 emerge from the open end of a lumen 83 a ofair conduit 83 from the junction box 18, and couple with the temperaturesensor 92. Inside the junction box 18, the leads 87, 89 are split fromthe air conduit 83 and coupled by a connector 95 with electrical cable21. More specifically, the leads 87, 89 exit from one arm of a tee 91that is otherwise sealed to prevent coolant air leakage.

Controller 27 (FIG. 3) operates the heating element 84 and alsoregulates the flow of coolant gas from the coolant fluid supply 85 tothe inlet coolant passageway 86 in order to maintain the nozzle tip 46and the viscous material resident in passageways 64 and 72 at a targetedtemperature, as represented by a temperature set point. When thetemperature is less than the set point, heat is supplied from theheating element 84 to the heat transfer member 44 and subsequentlyconducted to the nozzle 35 and to viscous material inside nozzle tip 46.When the temperature exceeds the set point, the heat transfer member 44is actively cooled by a flow of coolant gas through the annular plenum90, which subsequently cools the nozzle 35 and viscous material insidenozzle tip 46. In certain embodiments, the controller 27 automaticallyswitches between heating and cooling for precision temperatureregulation of the viscous material inside passageways 64 and 72 withoutmanual intervention and using only feedback temperature informationsupplied by temperature sensor 92. The invention contemplates that theactive cooling, which is illustrated as an air flow through passageways83 a and 86 and plenum 90, may be any cooling mechanism that reduces thetemperature of the heat transfer member 44 and/or nozzle 35 by removingheat from these structures.

The precise heating and active cooling of nozzle 35 and, in particular,nozzle tip 46 minimizes viscosity variations of the viscous materialresiding in passageways 64 and 72 for purposes of flowability anddispensing precise and reproducible amounts of viscous materials.However, the nozzle tip 46 is maintained below a temperature that maydegrade the properties of the viscous material, such as prematurelycausing either gelling or curing. Typically, the dispensability of theviscous material residing in the nozzle tip 46 is improved bymaintaining its temperature in a range between about 30° C. to about 65°C., although the temperature range is not so limited and may depend uponthe identity of the viscous material. The viscous material should bemaintained at the selected temperature range for only a brief period oftime and not to exceed a temperature at which curing may occur. For thisreason, only the nozzle assembly 34 is held at the temperature set pointand not the remainder of dispensing apparatus 10.

With reference to FIGS. 1-3, 3A, and 7, the solenoid valve 20 is mounteddirectly against the main body 22 with an intervening thermal barrier 96that prevents or, at the least, reduces heat transfer from the solenoidvalve 20 to the main body 22. Direct attachment of the solenoid valve 20to the main body 22 reduces the air volume thereby promoting a rapid airpressure change to actuate the air piston 78, which decreases theresponse time for filling the air cavity 80 to open and close thedispensing apparatus 10. Solenoid valve 20 typically includes a movablespool actuated by selectively energizing and de-energizing anelectromagnetic coil (not shown) with an electrical signal from a drivercircuit 20 a. The driver circuit 20 a is of a known design with a powerswitching circuit providing electrical signals to the solenoid valve 20.The driver circuit 20 a may be incorporated into the construction of thesolenoid valve 20.

In response to an electrical signal from the driver circuit 20 a, thesolenoid valve 20 selectively switches a flow path for pressurized airto an air supply port 101 between an air inlet port 99 and an airexhaust port 100. The supply port 101 communicates with air cavity 80through a passageway 98 defined in the main body 22. When a suitableelectrical signal is applied to solenoid valve 20, pressurized air issupplied from air inlet port 99 to supply port 101 and, subsequently, topassageway 98. A fluid path to exhaust port 100 is blocked inside thesolenoid valve 20. When the electrical signal is discontinued, air inletport 99 is blocked and exhaust port 100 is coupled with supply port 101.Pressurized air filling air cavity 80 is serially exhausted throughpassageway 98, supply port 101 and exhaust port 100.

The solenoid valve 20 may be any three-way or four-way valve thatoperates to switch a flow of pressurized air among flow paths asunderstood by those of ordinary skill in the art. A product line ofthree-way solenoid valves suitable for use as solenoid valve 20 indispensing apparatus 10 is the MHA2 product line of solenoid valves,commercially available from Festo Corporation of Hauppauge, N.Y.

With reference to FIGS. 3, 3A, and 7, air piston 78 defines anaxially-movable confinement wall of air cavity 80 and is pneumaticallysealed with the sidewall of air cavity 80. When the solenoid valve 20 isswitched by the electrical signal to fill the air cavity 80 withpressurized air through passageway 98, the air piston 78 and needle 24move axially in a direction that separates the needle tip 76 from thevalve seat 70 and thereby provides the opened position. Conversely, whenthe solenoid valve 20 is switched to exhaust the air cavity 80 ofpressurized air by removing the electrical signal, the air piston 78 andneedle 24 move axially in a direction that contacts the needle tip 76with the valve seat 70 and thereby provides the closed position.

The exhaust port 100 of the solenoid valve 20 is fluidically coupledwith an air passageway 102 in the main body 22 by a slotted channel 104formed in the thermal barrier 96. An opening 103 is also provided inthermal barrier 96 for coupling supply port 101 with passageway 98. Thepressurized air exhausted from the air cavity 80 is cooled by rapiddecompression of the air cavity 80 as the dispensing apparatus 10 closesand movement of air piston 78 toward its closed position. This cooledexhaust air from air cavity 80 is directed by the channel 104 betweenits opposite closed ends from the exhaust port 100 to the air passageway102 and subsequently to an air plenum 106 surrounding a length of theneedle 24. The exhaust air is ultimately routed to the ambientenvironment of dispensing apparatus 10 through an outlet passageway 108cross-drilled through main body 22, which has been rotated from itsactual angular orientation for clarity. The flow of cool exhaust airremoves heat from the needle 24 and main body 22. The heat is dumpedinto the ambient environment of dispensing apparatus 10 for disposal.The flow of cool exhaust air participates in precision regulation of thetemperature of the nozzle tip 46 by reducing conductive heat flow fromthe main body 22 and the needle 24 to the fluid chamber housing 28 andnozzle 35. This prevents or reduces the incidence of premature gellingand/or curing inside the main body 22. The channel 104 in the thermalbarrier 96 and air passageway 102 in the main body 22 cooperate tofurther reduce noise produced by the exhausted pressurized air byaltering the direction of the airflow.

The thermal barrier 96 and the active air flow of the cooled exhaust airthrough the passageways 102 and 108 and plenum 106 in the main body 22,considered either individually or collectively, assist in thermalmanagement of the heat load within the main body 22. As a result,extraneous heat sources do not influence or, at the least have a minimalinfluence on, the temperature of the nozzle 35 and the viscous materialresident therein during a dispensing cycle.

The solenoid valve 20 may be overdriven by the driver circuit 20 aenergizing the electromagnetic coil (not shown) of the solenoid valve 20in order to increase the operating speed of dispensing apparatus 10 bycausing faster acceleration of the air piston 78 from a stationarystate. The total response time for opening the dispensing apparatus 10is measured from the moment that an electrical signal is initiallyprovided to the solenoid valve 20 until the instant that the dispensingapparatus 10 is fully open. The total response time consists of acontribution from the solenoid response time required for the solenoidvalve 20 to switch and supply pressurized air at full flow to thepassageway 98 and a contribution from the fill time required to fill theair cavity 80 with pressurized air that terminates when the needle 24 isin a fully open position. The solenoid response time is reduced bycausing the driver circuit 20 a to place an overdriving voltage on theelectromagnetic coil during switching beyond a rated voltage for thesolenoid valve 20, which decreases the total valve response time. Forexample, a solenoid valve 20 rated for five (5) VDC may be energizedwith a voltage of twenty-four (24) VDC by the drive circuit 20 a todecrease response time and then modulated to maintain the solenoid valve20 in an opened state without damaging the solenoid valve 20. Inconjunction with the close coupling of the solenoid valve 20 to the mainbody 22, the overdriving of the driver circuit 20 a permits the aircavity 80 to be filled and the needle 24 to be placed in an openedcondition, including electrical response time of the solenoid valve 20,in less than four (4) milliseconds. The overdriving of the solenoidvalve 20 thereby reduces the total response time for opening thedispensing apparatus 10 by reducing the time contribution due to thesolenoid response relative to the time required to fill the air cavity80. The air cavity 80 is typically exhausted of air pressure and theneedle 24 moved to a closed condition in three (3) to four (4)milliseconds. This results in a maximum operating frequency of about 200Hz, as a portion of the time required to close the dispensing apparatus10 may overlap with the time required to open the dispensing apparatus10.

With reference to FIGS. 3 and 3A, a sonic muffler 110 may be provided inthe air passageway 102 in main body 22 for attenuating the sound wavesassociated with the exhausted air, which significantly reduces the noiserelated to air exhaust from air cavity 80 without significantlyretarding the closing response time of the air piston 78. The sonicmuffler 110 may be a porous structure formed, for example, from steelwool, polyethylene, or a metal such as bronze, steel, or aluminum, ormay constitute a baffle with internal passageways that slow airflow bydeflecting, checking, or otherwise regulating air flow in the airpassageway 102. The backpressure created by the sonic muffler 110 doesnot effect the response time for closing the dispensing apparatus 10 atthe associated air pressure within the air cavity 80. Because theexhaust port 100 of the solenoid valve 20 is fluidically coupled withair passageway 102 in the main body 22, a conventional muffler cannot beattached to the exhaust port 100.

A stroke adjust assembly includes a sleeve 116, a load screw 112threadingly engaged with sleeve 116, and a compression spring 114compressed by the load screw 112 for applying an axial load to a loadbutton 115 proximate to an end of the needle 24 opposite to the needletip 76. The load screw 112 is, which is secured to the main body 22through sleeve 116, and is movable axially by rotation relative to mainbody 22. The compression spring 114 is partially compressed and therebypreloaded by adjustment of the axial position of the load screw 112relative to the sleeve 116. After this preloaded spring bias is set, atreadlocker is applied to permanently fix the relative positions of theload screw 112 and sleeve 116.

A stroke adjust knob 118 is affixed to the load screw 112 and,thereafter, is used to rotate load screw 112 and sleeve 116 relative tothe main body 22 for defining a stroke length for the needle tip 76relative to the valve seat 70. The dispensing apparatus 10 is depictedin FIG. 3 with a zero stroke length setting and the maximum preloadspring bias. Setting the stroke length modifies the magnitude of thepreloaded spring bias.

When sufficient pressurized air is supplied to air cavity 80 forovercoming the preloaded spring bias, air piston 78 will carry needle 24and the load button 115 in a direction away from valve seat 70. Contactbetween load button 115 and sleeve 116 operates as a stop. As a result,the needle tip 76 separates from the valve seat 70 and a small amount ofviscous material flows into fluid passageway 64 in the valve seat disk62. When air pressure is exhausted from air cavity 80, the axial loadfrom spring 114 rapidly moves the needle 24 toward the valve seat 70,which forces a small amount of viscous material resident in passageway72 out of discharge orifice 74.

The preloading spring bias, as modified by the stroke adjust setting, isconserved when heat transfer member 44, the nozzle 35, and/or the fluidchamber housing 28 are removed from dispensing apparatus 10 andreplaced, such as during cleaning and maintenance. As a result, thepreloading spring bias will not normally need to be readjusted from thevalue set at the time of manufacture and/or before the dispensingapparatus 10 is placed into operation. The ability to preserve thepreloading spring bias of spring 114 eases re-assembly and installation.

The needle 24 is guided during its reciprocating axial movement withinthe main body 22 by a pair of axially spaced needle guides or bushings122, 124, of which bushing 124 is positioned in a bearing sleeve 125.Bushings 122, 124 may be formed from plastic, such as PEEK containinggraphite that operates as a lubricant. The axial spacing of the bushings122, 124 is selected to be at least four (4) times the diameter of theportion of the needle 24 therein, which advantageously provides andmaintains accurate axial guidance of the needle tip 76 for repeatedcontact and sealing with the valve seat 70 over multiple dispensingcycles. A fluid seal 126 surrounding a portion of the needle 24 and afluid seal 128 surrounding a different portion of the needle 24 isolatethe fluid chamber 60 and the air cavity 80, respectively, from theportion of bore 26 between bushings 122, 124.

With reference to FIG. 8 in which like reference numerals refer to likefeatures in FIGS. 1-7 and in accordance with an alternative embodimentof the invention, a liner 130 may be positioned inside of the fluidchamber housing 28. Liner 130 acts as a fluid barrier that preventswetting of the interior surfaces 131 of the fluid chamber housing 28.The liner 130 is removable from the fluid chamber housing 28 and, hence,replaceable. Therefore, these interior surfaces 131 do not have to becleaned when the fluid chamber housing 28 is removed from the main body22 and is readily reusable by simply inserting a fresh or clean liner130.

Liner 130 may be formed from any suitable material including, but notlimited to, aluminum and polymers like nylon. The liner 130 may becleaned and reused, or may simply be discarded if formed from arelatively inexpensive material. The liner 130 is illustrated asincluding an integral valve seat disk 132, fluid fitting 134, and afluid seal 135 which are removable along with the liner 130, althoughthe invention is not so limited.

With reference to FIGS. 9A and 9B in which like reference numerals referto like features in FIGS. 1-7 and in accordance with an alternativeembodiment of the invention, a valve seat disk 136 similar to valve seatdisk 62 (FIGS. 5A and 5B) and suitable for use with dispensing apparatus10 (FIG. 1) includes a discharge passageway 138 having an outlet 140 andan inlet 142. In the closed position, the needle tip 76 (FIG. 5A)contacts a frustoconical surface 144 across a valve seat 146 that isspaced from inlet 142. The geometrical shape of the valve seat 146 maybe defined by plastic deformation or coining due to repeated contactbetween the needle tip 76 and the frustoconical surface 144. The valveseat 146 may widen during operation of the dispensing apparatus 10(FIG. 1) due to gradual wear of the frustoconical surface 144 by thereciprocating action of the needle tip 76 relative to the valve seat 146and the presence of abrasives in the viscous material being dispensed.Because the valve seat 146 is spaced from the inlet 142, geometricalchanges in the valve seat 146 due to contact by needle tip 76 do notsignificantly impact the inlet 142. The valve seat disk 136 may beformed from the same material as valve seat disk 62 or, alternatively,valve seat disk 136, or at least the frustoconical surface 144, may becoated with a substance in this hardness range. This may be beneficialwhen dispensing viscous materials that are abrasive, as the wear offrustoconical surface 144 will be reduced.

The portion of the frustoconical surface 144 defining valve seat 146 maybe plastically deformed to define the initial valve seat 146, beforevalve seat disk 136 is installed in the dispensing apparatus 10 andcontacted by the needle tip 76 in the closed position. This pre-usedimpling increases the area of the valve seat 146 contacted by needletip 76. The rate of the initial wear of a non-dimpled valve seat, ifallowed to occur in the dispensing apparatus 10, is significantlygreater than the subsequent wear rate. Pre-use dimpling of frustoconicalsurface 144 to define the initial valve seat 146 operates to flatten thewear curve so that the higher initial wear is not experienced when thevalve seat disk 136 is initially installed in the dispensing apparatus10. Pre-use dimpling permits the liquid dispenser 10 to operate in thelower linear regime immediately upon installation without experience theinitial higher and/or non-linear wear rate.

With reference to FIG. 10 and in accordance with an alternativeembodiment of the invention, a heater 150 may be positioned about alength of the fluid tube 56 for applying heat to elevate the temperatureof the viscous material being transferred through tube 56 to the mainbody 22 (FIG. 3). The heater 150 includes a thermally-conductive blockor body 152 that mounts onto the fluid tube 56 with a good thermalcontact. Positioned in thermal contact with the body 152 and withincorresponding blind bores are a heating element 154 and a temperaturesensor 156. Electrical leads extend from the heating element 154 and thetemperature sensor 156 to controller 27. The body 152 may have aclamshell-style construction with a groove formed in each shell half 152a, 152 b into which the fluid tube 56 is received with a contacteffective for heat transfer. The heat supplied by heater 150 to theviscous material in side fluid tube 56 supplements the heating of theviscous material in the nozzle 35 (FIG. 3A) and may be particularlyuseful for dispensing at high flow rates in which the flow of viscousmaterial through the discharge passageway 72 (FIG. 4) is too fast foreffective temperature control by heat transfer within nozzle 35 alone.

With reference to FIG. 11 in which like reference numerals refer to likefeatures in FIG. 3A and in accordance with alternative embodiment of theinvention, heat transfer member 44 may include an annular internalplenum 160 coupling the inlet and outlet passageways 86, 88. The plenum160 extends circumferentially about the heat transfer member 44 and, asa result, encircles or surrounds an axial length of the nozzle mount 48.Coolant gas supplied from air conduit 83 to inlet passageway 86 flowsthrough plenum 160 and is exhausted through the outlet passageway 88 tocreate a positive fluid flow. The internal plenum 160 may be implementedeither individually or in combination with plenum 90 (FIG. 3A).

While the present invention has been illustrated by a description ofvarious embodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand methods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicants' general inventive concept. The scope ofthe invention itself should only be defined by the appended claims,wherein we claim:

1. An apparatus for dispensing a viscous fluid in a noncontact manner,comprising: a supply of viscous material; a coolant fluid source capableof supplying a coolant fluid; a nozzle assembly including a dischargepassageway, a heat transfer member, a temperature sensor thermallycoupled with said heat transfer member, a first fluid passageway in saidheat transfer member and coupled in fluid communication with saidcoolant fluid source to direct a flow of the coolant fluid to said firstfluid passageway, a plenum connected in fluid communication with saidfirst fluid passageway for receiving the flow of the coolant fluid, anda second fluid passageway in said heat transfer member and coupled influid communication with said plenum for exhausting the flow of thecoolant fluid from said plenum, the plenum extending at least partiallyaround said nozzle assembly; a fluid chamber housing, said fluid chamberhousing including a fluid chamber, said fluid chamber being in fluidcommunication with said discharge passageway and said supply of viscousmaterial; a main body containing a part of a valve element, a part ofsaid valve element extending through said fluid chamber, said valveelement having an opened position in which the viscous material isallowed to flow from said fluid chamber into said discharge passagewayand a closed position in which the viscous material is blocked fromflowing from said fluid chamber into said discharge passageway; and acontroller electrically coupled with said temperature sensor and withsaid coolant fluid source, said controller causing said coolant fluidsource to supply the coolant fluid to said heat transfer member andthereby cool at least a part of said nozzle assembly in response totemperature signals received from said temperature sensor.
 2. Theapparatus of claim 1 wherein said nozzle assembly further comprises: aheating element operatively coupled with said controller and thermallycoupled with said heat transfer member, said controller causing saidheating element to heat said heat transfer member and at least a part ofsaid nozzle assembly in response to temperature signals received fromsaid temperature sensor.
 3. The apparatus of claim 2 wherein theapparatus is configured to jet a droplet of the viscous material fromsaid discharge passageway as the valve element is moved from the openedto the closed position.
 4. The apparatus of claim 2, wherein said mainbody includes an air cavity, and said valve element is movable betweenthe opened and closed positions by selective application of pressurizedair to said air cavity, and further comprising: a solenoid valve havingan exhaust port selectively coupled in fluid communication with said aircavity, said solenoid valve configured to direct the pressurized airfrom said air cavity to said exhaust port to permit movement of saidvalve element from said opened to said closed position; and an airpassageway extending through said main body, said air passageway coupledby said exhaust port of said solenoid valve with said air cavity of saidmain body so that pressurized air exhausted from said air cavity flowsthrough said air passageway to cool said main body.
 5. The apparatus ofclaim 4, wherein said apparatus is configured to jet a droplet of theviscous material from said discharge passageway as said valve element ismoved from the opened position to the closed position.
 6. The apparatusof claim 1 wherein said main body includes an air cavity, and said valveelement is movable between the opened and closed positions by selectiveapplication of pressurized air to said air cavity, and furthercomprising: a solenoid valve having an exhaust port selectively coupledin fluid communication with said air cavity, said solenoid valveconfigured to direct the pressurized air from said air cavity to saidexhaust port to permit movement of said valve element from said openedcondition to said closed position; and an air passageway extendingthrough said main body, said air passageway coupled by said exhaust portof said solenoid valve with said air cavity of said main body so thatpressurized air exhausted from said air cavity flows through said airpassageway to cool said main body.
 7. The apparatus of claim 6, whereinsaid apparatus is configured to jet a droplet of the viscous materialfrom said discharge passageway as said valve element is moved from theopened to the closed position.
 8. The apparatus of claim 1 wherein saidfluid chamber housing is attached to said main body.
 9. The apparatus ofclaim 8 wherein said nozzle assembly is releasably attached to saidfluid chamber housing.
 10. The apparatus of claim 8 wherein said fluidchamber housing is releasably attached to said main body.
 11. Theapparatus of claim 1 wherein said plenum is annular.